Stump grinders are well known devices that employ a pivotal grinding arm that carries a rotatable grinding wheel at its outer end. The grinding wheel extends generally vertically and has powered rotation about a substantially horizontal axis of rotation. The pivotal grinding arm is pivotal on a support frame in an up and down motion about a substantially horizontal axis. In addition, the grinding arm is also pivotal in a side-to-side motion about a substantially vertical axis in many stump grinders.
When the grinding wheel is placed into operation and is rotating in a vertical plane about its substantially horizontal axis of rotation, the operator can pivot the grinding arm up and down and from side-to-side. This causes the grinding wheel to bite into and traverse over the stump or other wood debris that is to be grinded into particles. As repeated passes of the grinding arm and grinding wheel are made relative to the stump or other wood debris, the action of the grinding wheel gradually reduces the stump or wood debris to small wood chips or fine particles.
Stump grinders typically have the pivotal grinding arm and the grinding wheel arranged generally symmetrically with respect to the lateral width of the frame of the stump grinder. Thus, for an operator who is standing behind the frame or is carried on the frame on some type of seat or operator's platform, the grinding arm is usually disposed in a home position that is centered on the stump grinder frame and extends away from the operator in a straight fore-and-aft direction. The grinding arm traverses from side-to-side in generally equal arcs to either side of the home position. However, in this centered home position, the view of the operator with respect to the action of the grinding wheel on the stump or wood debris can be blocked or obstructed by the structure of the grinding arm itself. In other words, the operator may not be able to clearly see the contact area between the grinding wheel and the stump or wood debris.
In addition, the task of operating the stump grinder can involve multiple controls that can be difficult or at least confusing for the operator to use. There must be a set of traction and steering controls for the operator to use to control the forward and reverse motion of the stump grinder frame and to steer or turn the stump grinder frame. In addition, there must be other grinding arm controls to allow the operator to manipulate the grinding arm to cause the grinding arm to pivot up and down and to traverse from side-to-side out of the centered home position. There must also be an on-off grinding control to start or stop the rotation of the grinding wheel on the grinding arm.
Typically, the grinding arm controls often take the form of multiple levers. One lever controls the up and down motion of the grinding arm. Another lever controls the side-to-side traverse. The on-off grinding control often comprises yet another separate control, i.e. a separate on-off switch. Needless to say, it is not an easy task for the operator, particularly an unskilled operator who might rent a stump grinder from a rental business and is thus somewhat unfamiliar with the controls, to coordinate and properly use all of the multiple controls typically found on a stump grinder.
Finally, it should be apparent that the grinding wheel of a stump grinder should be reliably and durably driven in a cost-effective and simple manner. Mechanical drive systems, such as belt or chain drives, are prone to breaking given the forces involved in stump grinding and are costly and time consuming to maintain and to keep properly adjusted. Hydraulic motors carried on the grinding arm have been used to directly drive or rotate the grinding wheel without the interposition of belt or chain drives. However, the high forces involved in grinding that are transmitted to the shaft of such a hydraulic motor often exert large loads on the motor, leading to premature wear and failure of the motor. Given the relatively high cost of such hydraulic motors, this is a disadvantage of known designs in which hydraulic motors have been used to directly drive the grinding wheels.